The front structure of a vehicle generally absorbs energy using horizontal tubular columns oriented parallel to the vehicle fore-aft axis. These columns collapse axially within a mode which has localized buckling and collapse. The goal is to maximize the energy absorbed which is equal to the crush force (P) times deflection (D), PxD. The P force is dictated by the G curve that is acceptable for the occupant. Assuming a square wave pulse curve, the maximum G load will be about 20 G. The deflection allowable from the structure will be about 0.8 times the crush length, 0.8 L.
Angular energy (30.degree. angular) is absorbed by bending the front structure of the vehicle. An offset load generally buckles the front frame members in a Euler column manner at their bases at the engine cross member. The longer the columns, the more likely the buckling and the lower the energy taken out by the buckling. Longer columns are desirable for frontal energy absorption, but detrimental to angular energy absorption.
One approach to the angular energy absorption is to design a front end beam structure to tie the left and right frame members together. A cross beam properly attached will cause both the left and right frame members to be involved in angular energy absorption. The energy absorbed with the beam structure is significantly more than without a beam structure. Nonlinear finite element analysis has shown the energy absorbed to be twice as high in a 30.degree. angular energy absorption test with a beam.
While the beam improves angular energy absorption, it hinders frontal energy absorption because the beam, when tied conventionally to the front structure, reduces the amount of the front crush and thus requires that the vehicle be lengthened the width of the beam. The added length decreases vehicle aesthetics, function, weight and cost. Accordingly, it will be appreciated that it would be highly deskable to have a front beam structure to tie the left and right frame members together without reducing the frontal crush. It is also desirable to have a structure that ties the left and right frame members together without decreasing the vehicle aesthetics, function, weight or cost.